Unlike time-domain interpolation [270], ideal
spectral interpolation is very easy to implement in practice by means of
zero padding in the time domain.
That is,

Since the frequency axis (the unit circle in the
plane) is finite
in length, ideal interpolation can be implemented exactly to
within numerical round-off error. This is quite different from ideal
(band-limited) time-domain interpolation, in which the interpolation
kernel is
sinc
; the
sinc
function extends to plus and
minus infinity in time, so it can never be implemented exactly in
practice.3.9